Polymers are employed in the technical realm especially as potting compounds for electric machines, printed circuit boards or electric modules, but also as an adhesive structure and as a coating, for example, in the form of protective lacquers. Many material groups of the components involved often show signs of corrosion or swelling when they come into contact with oily and/or aqueous solutions. One example of this is so-called copper corrosion, which frequently occurs when electric and/or electronic components come into contact with the media needed for the proper functioning. In the area of the adhesive structure, in contrast, problems occur especially when moisture penetrates between the contact areas of the polymer and the component, where it causes corrosion, decomposition and swelling which, in turn, can cause the destruction of the adhesive bond and of the component. Such problems are particularly relevant in the realm of electric machines.
Electric machines (electromechanical converters) such as, for instance, electric drive motors for motor vehicles, starters, generators or starter-generators, convert electric energy into mechanical energy (motors) or mechanical energy into electric energy (generators). This electromechanical conversion is based on electromagnetic induction. Such electric machines comprise a stationary stator (stand) which, in a familiar design, encompasses a stator core (core stack) with corresponding wire windings and one or more connector rings arranged thereupon as well as a movable component which, in the most common design, is configured as a rotor (armature) which is rotatably mounted in or around the ring-shaped stator and which has a plurality of permanent magnets. In this context, the moving magnetic field of the rotor generates a current flow in the stator winding (generator) or else the magnetic field generated by the stator brings about the mechanical movement or rotation of the rotor (motor). Opposite designs are likewise known, in which the rotor comprises a winding while the stator comprises magnets.
Parts of the stator and/or rotor containing the winding and the connector ring are embedded in a potting compound in order to provide them with electric insulation and mechanical protection as well as protection against chemical effects. The potting compound is especially used to embed the connector ring (also referred to as an interconnecting ring or contact bridge) which electrically connects the individual windings to each other. Typically, potting compounds are based on silicone rubber. In order to increase their thermal conductivity, these silicone elastomers often contain an additive with large fractions of fillers, for example, in the form of quartz particles. Such materials meet most of the technical requirements made of potting compounds; in particular, they exhibit very low electric conductivity, high thermostability and resistance to cyclic temperature stress, high thermal conductivity, high oxidation stability, good substrate adhesion as well as a simple curing and a high level of processing tolerance. A problem, however, is the high affinity of silicones to hydrocarbons. They display the tendency to pick up motor oil and transmission oil, swelling up in the process. The swelling, however, detrimentally affects the mechanical properties. For instance, the strength and material hardness diminish, which can cause a drop in the thermostability as well as detachment and conceivably brittleness of the potting compound. Especially when it comes to oil-cooled electric motors, whose design means that they come into contact with transmission oils, it would therefore be desirable to reduce or prevent oil absorption and oil swelling by the silicone material.
Problems can also be caused by media penetrating into the area of the adhesive structure for the magnet on the rotor or stator. The adhesives used for the magnets especially include silicone resin systems which are partially filled with glass beads that act as spacers so as to ultimately allow the thickness of the adhesive film to be established. As a matter of principle, the adhesive structure for the magnet has to meet the same technical requirements as the potting compound does (see above) and it additionally has to display a good adhesive effect. In particular, here too, the silicone resin system employed should not be affected by the penetration of moisture or oil, which would diminish the adhesive strength.
German patent specification DE 31 33 734 C2 describes an electric insulation for the winding overhang of a stator or rotor of an electric machine which, at the same time, provides protection against moisture. The coating contains a silicone rubber as the basic material containing rod-shaped copolymers on the basis of styrene-butyl acrylate instead of a mineral filling material.
German patent application DE 10 2005 017 113 A1 discloses a two-layer protective layer arrangement for the winding overhang of an electric machine whose first layer has a gel-like configuration and consists primarily of silicone gel, and whose second layer is harder than the first one. Both layers can consist of silicone rubber although, as an alternative, the second layer can consist of cast resin.
Moreover, the hydrophobic effect of compounds containing fluorine is known from many technical sectors. For example, textiles coated with PFTE or else fluorocarbon chains are covalently bonded to the fibers in order to produce both hydrophobic and, at the same time, oleophobic surfaces. A process likewise known from the textile industry is the application of silicone-based and fluorocarbon-based hydrophobic coatings onto textiles. In the case of synthetic fibers made of polyolefins or polyesters, gas-phase fluorination is additionally employed, involving a complex combination of plasma treatment, air supply, grafting of fluorocarbon monomers and subsequently another plasma treatment in a CF4-atmosphere (U.S. Pat. Appln. Pub. No. 2011/045200 A1).
U.S. Pat. No. 5,416,373 describes a winding for a stator or rotor of an electric machine in which the winding is coated with an electrically insulating film or with a mica tape. An additional coating containing fluorine is applied in the exposed area of the winding overhang in order to protect the winding against moisture.
German patent application DE 10 2005 017 112 A1 likewise describes a protective two-layer arrangement for the winding overhang of an electric machine. The protective layer arrangement comprises a first layer of highly elastic silicone gel adjoining the conductor arrangement of the winding overhang as well as an outer layer containing silicone rubber as the basic material, to which the fine-grained, surface-modified perfluorinated compounds having a particle diameter of about 10 nm have been added. The coating has a nanostructured surface superimposed with a microstructure, and it is characterized by a high degree of hydrophobicity, with water-contact angles of at least 120°.